PHYS 252 TEST #1 1/23/08 Dr. Holmes NAME___ ______________
DO ALL 8 PROBLEMS. THE WORTH OF EACH
PROBLEM IS MARKED BESIDE THE PROBLEM. SHOW YOUR WORK FOR PARTIAL CREDIT.
1) Given the following wavelengths in
air, identify the type of light (microwave, ultraviolet, etc. - if visible,
identify the color: red, green, etc.) and the frequency of the light.
Wavelength TYPE FREQUENCY
a) 3x10+2 meters radio (AM) 1.0 x 106 Hz = 1 MHz
b) 4x10-2 meters microwave 7.5 x 109 Hz = 7.5 GHz
c) 5x10-4 meters microwave/IR 6.0 x 1011 Hz
d) 6x10-5 meters IR 5.0
x 1012 Hz
e) 5x10-7 meters visible: blue/green 6.0 x 1014 Hz
f) 4x10-10 meters UV/x-ray 7.5 x 1017 Hz
2) a) What is the speed of light in vacuum?
3 x 108 m/s
b) What is the speed of light in glass
(given that the glass has an index of refraction of 1.87) ?
1.6 x 108 m/s
c) Given that the wavelength of a ray of
light in the glass is 500 nm, what is the wavelength of the wave in the air?
935 nm
d) Given that the wavelength of a ray of
light in the glass is 500 nm, what is the frequency of the wave in glass?
3.2 x 1014 Hz
e) Does the type of light (e.g., microwave,
x-ray, or if visible, the color) change when it goes from air to glass?
No
f) What type is this ray of light
(microwave, x-ray, etc. and if visible, what color: green, blue, etc.) ? [If
your answer to part e was yes, assume the light is in the glass.]
IR
3) A ray of light in glass (assume n = 1.87
for glass) hits a glass/air (assume n = 1.00 for air) interface at an angle of
77 degrees with respect to the SURFACE of the interface.
a) What is the angle of reflection measured
from the SURFACE?
77 degrees
b) What is the angle the transmitted ray in
the air makes with the NORMAL (if totally reflected, answer TIR)?
24.9 degrees
c) Can rays of light in the glass be totally
reflected from the glass/air interface?
Yes
d) Can rays of light in the air be totally
reflected from the air/glass interface?
No
4) A lens is made from glass of index of
refraction 1.87 . Its front lens has a radius of curvature of +7 cm, and its
back surface has a radius of curvature of -15 cm.
a) DRAW A PICTURE of this lens on the right
side of this problem. Be sure to show relative curvatures.
b) Is the lens converging or diverging?
Converging
c) What is the focal length of this lens?
15.1 cm (if drawn like a contact lens)
d) If the lens had a back surface of radius
of curvature of +15 cm, what would its focal length be?
+5.49 cm (if the lens is fully convex).
5) a) Draw a diagram showing the eye, lens,
object and image for a person wearing glasses to correct for near-sightedness:
b) If the person with near-sightedness can
make out an object as far as (but no farther than) 45 cm without
glasses, what should the focal length of his glasses be if the person is to
make out an object that is 100 meters away?
-45.2 cm
c) DESIGN a lens that has the above focal
length (from part b) and DRAW A PICTURE of the lens making sure to show
relative curvatures.
nglass =
R1 =
R2 =
Picture:
Many answers possible - you need to
determine one that gives correct answer.
6) A magnifying glass has a focal length of
2.1 cm. a) What is the magnification of this lens when used
properly?
12.9 X
b) What should the image distance be if it is
used "properly".
-25 cm
c) DRAW A DIAGRAM showing the object, lens,
image, eye, and focal points for the lens.
7) A 35 mm camera (film is 24mm x 36mm) has
a regular lens of focal length 55 mm. A photographer takes a picture of a
friend who stands 170 cm (»5'7") tall. a) If the photographer
is 3 meters from the friend, what should be the distance from the film to the
lens?
56.03 mm.
b) What is the image size on the film?
-31.7.0 mm
c) Could the photographer get all of the
friend on the film? (Assume the photographer can turn the camera so as to use
the long side [36mm] of the film.)
Yes (but your answer depends on your
answer to b above)
8) DESIGN a microscope to have a magnifying
power of 325 (that is, specify the following):
M = -325
L =
fobj =
feye =
sobj =
s'obj =
seye =
s'eye =
Many answers are possible. You need to
specify one that works correctly
Draw a diagram of the microscope, and
indicate on the diagram the quantities: L, sojb , s'obj ,
seye , and s'eye ; also show where the Object is and
where the final Image is.